Rolling resistance of a tire may be defined as the amount of energy dissipated in rolling of the tire per unit normal load and unit distance travelled by the tire. For a tire made of rubber, the main contributor to rolling resistance is hysteresis due to the viscoelastic behavior of rubber. Repeated cycles of deformation and recovery experienced by a rubber tire as it rotates under the weight of a vehicle leads to hysteresis energy loss being dissipated from the rubber tire as heat. The rolling resistance may cause an increase in fuel consumption and vehicle greenhouse gas emissions. Therefore, there is a need for designing rubber tires with lower rolling resistance. To this end, systems and methods are required for measuring and comparing rolling resistances and energy dissipations in rubber tires under rolling conditions.
Developing systems and methods for measuring the rolling resistance of a rubber tire may have numerous challenges such as finding optimal ways of applying the rolling driving force, measuring the rolling resistance, and providing a continuous flat surface for rolling. Systems and methods have been developed in which rubber tires are rolled against a rotating drum using complex mechanical and electronic devices to apply the rolling driving force and measuring the rolling resistance. However, in such systems and methods due to the complexity of the system, losses in gears and motors may not be properly accounted for, which may considerably affect the accuracy of the measurements.
In order to replace the complex mechanical and electronic devices in the aforementioned measuring systems, an independent pendulum driving force may be utilized to create a reciprocating rolling movement that may simulate a continuous rolling motion of the rubber tire. Damping of the oscillatory motion of the rubber tire that is connected to the pendulum may be utilized for measuring the rolling resistance of the rubber tire. However, systems and methods that are developed based on damping of oscillatory motion of a pendulum need to be further improved to ensure a repeatable release of the pendulum at a specific angle, a straight rolling path for the rubber tire, and a balanced pendulum motion against centrifugal forces acting on the pendulum. There is further a need for developing systems and methods that allow for an accurate non-contact measurement of rolling resistance without imposing unwanted limitations in the oscillatory rolling motion of the rubber tire.